Fluororubber composition

ABSTRACT

The present invention provides a fluororubber composition that has excellent heat resistance and excellent mechanical properties at high temperatures. The fluororubber composition comprises a peroxide cross-linkable fluororubber (A); a carbon black (B); a peroxide cross-linking agent (C); and a low-self-polymerizing cross-linking accelerator (D), wherein to 100 parts by mass of the fluororubber (A), the amount of the carbon black (B) is 5 to 50 parts by mass, the amount of the cross-linking agent (C) is 0.01 to 10 parts by mass, and the amount of the cross-linking accelerator (D) is 2.5 parts by mass or smaller.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit under 35 U.S.C. §119(e) of U.S.Provisional Application No. 61/377,017 filed on Aug. 25, 2010,incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a fluororubber composition giving across-linked product that has excellent mechanical properties at hightemperatures.

BACKGROUND ART

Fluororubbers are known to be excellent in chemical resistance, oilresistance, and heat resistance, and also to have good compression setresistance at high temperatures. Fluororubbers are now desired to havebetter mechanical properties at high temperatures, such as strength athigh temperature and elongation at high temperature. For example, when across-linked fluororubber product is used at as high temperature as morethan 100° C., the product is required to have excellent mechanicalproperties at high temperatures as well as heat resistance, for highdurability.

In terms of an increase in the compression set resistance, compositionssuch as one taught in Patent Document 1 have been proposed. Thosecompositions, however, have low elongation at room temperature, andtherefore will probably have lower elongation at high temperature. Thecomposition described in Patent Document 2 has higher elongation at hightemperature, but does not have resistance to more severe useenvironment. The combination of a fluororubber and a thermoplasticfluoroelastomer in Patent Document 3 is an example of higher strength athigh temperature, but the elongation at room temperature of thiscomposition is also low, and therefore the elongation at hightemperature will probably be even lower.

-   Patent Document 1: JP S60-55050 A-   Patent Document 2: JP 2008-184496 A-   Patent Document 3: JP H06-25500 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention aims to provide a fluororubber composition givinga cross-linked product that has excellent heat resistance and excellentmechanical properties at high temperatures.

Means for Solving the Problems

That is, the present invention relates to a fluororubber compositioncomprising:

a peroxide cross-linkable fluororubber (A);

a carbon black (B);

a peroxide cross-linking agent (C); and

a low-self-polymerizing cross-linking accelerator (D),

wherein to 100 parts by mass of the fluororubber (A), the amount of thecarbon black (B) is 5 to 50 parts by mass, the amount of thecross-linking agent (C) is 0.01 to 10 parts by mass, and the amount ofthe cross-linking accelerator (D) is 2.5 parts by mass or smaller.

The carbon black (B) is preferably a carbon black having a nitrogenadsorption specific surface area (N₂SA) of 5 to 180 m²/g and a dibutylphthalate (DBP) oil absorption of 40 to 180 ml/100 g.

The fluororubber (A) is preferably a vinylidene fluoride copolymerrubber, a tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymerrubber, or a tetrafluoroethylene/propylene copolymer rubber, in terms ofgood heat resistance (heat-aging resistance) and oil resistance.

The cross-linking accelerator (D) is preferably trimethallylisocyanurate.

The amount of the cross-linking accelerator (D) is preferably 2.0 partsby mass to 100 parts by mass of the fluororubber (A).

The fluororubber composition before cross-linking preferably has adifference δG′ (G′(1%)−G′(100%)) of 120 kPa or higher and 3,000 kPa orlower,

the difference determined by subtracting the shear modulus G′(100%) at100% dynamic strain from the shear modulus G′(1%) at 1% dynamic strainin a dynamic viscoelasticity test with a rubber process analyzer (RPA)under the conditions of a measurement frequency of 1 Hz and ameasurement temperature of 100° C.

The present invention also relates to a cross-linked fluororubberproduct obtained by cross-linking the fluororubber composition of thepresent invention which includes the cross-linking agent (C) and thecross-linking accelerator (D).

The cross-linked fluororubber product preferably has a loss modulus E″of 400 kPa or higher and 6,000 kPa or lower determined by a dynamicviscoelasticity test under the conditions of a measurement mode oftensile, a chuck distance of 20 mm, a measurement temperature of 160°C., a tensile strain of 1%, an initial force of 157 cN, and a frequencyof 10 Hz.

Further, the cross-linked fluororubber product preferably has a storagemodulus E′ of 1,500 kPa or higher and 20,000 kPa or lower determined bya dynamic viscoelasticity test under the conditions of a measurementmode of tensile, a chuck distance of 20 mm, a measurement temperature of160° C., a tensile strain of 1%, an initial force of 157 cN, and afrequency of 10 Hz.

Effect of the Invention

The present invention can provide a fluororubber composition giving across-linked product that has excellent heat resistance and excellentmechanical properties at high temperatures.

Mode(s) for Carrying Out the Invention

The fluororubber composition of the present invention comprises:

a peroxide cross-linkable fluororubber (A);

a carbon black (B);

a peroxide cross-linking agent (C); and

a low-self-polymerizing cross-linking accelerator (D),

wherein to 100 parts by mass of the fluororubber (A), the amount of thecarbon black (B) is 5 to 50 parts by mass, the amount of thecross-linking agent (C) is 0.01 to 10 parts by mass, and the amount ofthe cross-linking accelerator (D) is 2.5 parts by mass or smaller.

Each of the elements will be described hereinbelow.

Peroxide Cross-Linkable Fluororubber (A)

The fluororubber (A) in the present invention may be any peroxidecross-linkable fluororubber, and preferably has a structural unitderived from at least one monomer selected from the group consisting oftetrafluoroethylene (TFE), vinylidene fluoride (VdF), andperfluoroethylenic unsaturated compounds (e.g. hexafluoropropylene (HFP)and perfluoro(alkyl vinyl ether) (PAVE)) represented by formula (1):CF₂═CF—R_(f) ^(a)  (1)wherein R_(f) ^(a) is —CF₃ or —OR_(f) ^(b) (R_(f) ^(b) is a C1-C5perfluoroalkyl group).

In another aspect, the fluororubber is preferably a non-perfluorofluororubber or a perfluoro fluororubber.

Examples of the non-perfluoro fluororubber include: vinylidene fluoride(VdF) fluororubber; tetrafluoroethylene (TFE)/propylene (Pr)fluororubber; tetrafluoroethylene (TFE)/propylene (Pr)/vinylidenefluoride (VdF) fluororubber; ethylene (Et)/hexafluoropropylene (HFP)fluororubber; ethylene (Et)/hexafluoropropylene (HFP)/vinylidenefluoride (VdF) fluororubber; ethylene (Et)/hexafluoropropylene(HFP)/tetrafluoroethylene (TFE) fluororubber; fluorosiliconefluororubber; and fluorophosphazene fluororubber. Each of these may beused alone, or any of these may be used in combination to the extentthat they do not deteriorate the effects of the present invention. Moresuitable among these are VdF fluororubber, TFE/Pr rubber, and TFE/Pr/VdFrubber because of their good heat-aging resistance and oil resistance.

The VdF rubber preferably has 20 mol % or more and 90 mol % or less, andmore preferably 40 mol % or more and 85 mol % or less, of a VdFrepeating unit in the total moles of the VdF repeating unit andrepeating units derived from other comonomers. The lower limit thereofis further preferably 45 mol % and particularly preferably 50 mol %,while the upper limit thereof is further preferably 80 mol %.

The comonomers in the VdF rubber are not particularly limited as long asthey are copolymerizable with VdF. Examples thereof includefluoromonomers such as TFE, HFP, PAVE, chlorotrifluoroethylene (CTFE),trifluoroethylene, trifluoropropylene, tetrafluoropropylene,pentafluoropropylene, trifluorobutene, tetrafluoroisobutene,hexafluoroisobutene, vinyl fluoride, iodine-containing fluorinated vinylether, and a fluoromonomer represented by formula (2):CH₂═CFR_(f)  (2)wherein R_(f) is a C1-C12 linear or branched fluoroalkyl group;fluorine-free monomers such as ethylene (Et), propylene (Pr), and alkylvinyl ethers; monomers giving a cross-linkable group (a curing site);and a reactive emulsifier. Each of these monomers and compounds may beused alone, or two or more of these may be used in combination.

The PAVE is more preferably perfluoro(methyl vinyl ether) (PMVE) orperfluoro(propyl vinyl ether) (PPVE), and is particularly preferablyPMVE.

The PAVE may be a perfluoro vinyl ether represented by the formula:CF₂═CFOCF₂OR_(f) ^(c)wherein R_(f) ^(c) is a C1-C6 linear or branched perfluoroalkyl group, aC5-C6 cyclic perfluoroalkyl group, or a C2-C6 linear or branchedperfluorooxyalkyl group having 1 to 3 oxygen atoms. The PAVE ispreferably CF₂═CFOCF₂OCF₃, CF₂═CFOCF₂OCF₂CF₃, or CF₂═CFOCF₂OCF₂CF₂OCF₃.

The fluoromonomer of formula (2) is preferably a monomer in which R_(f)is a linear fluoroalkyl group, and more preferably a monomer in whichR_(f) is a linear perfluoroalkyl group. The carbon number of R_(f) ispreferably 1 to 6. Examples of the fluoromonomer of formula (2) includeCH₂═CFCF₃, CH₂═CFCF₂CF₃, CH₂═CFCF₂CF₂CF₃, and CH₂═CFCF₂CF₂CF₂CF₃.Preferable among these is 2,3,3,3-tetrafluoropropylene represented asCH₂═CFCF₃.

The VdF rubber is preferably at least one copolymer selected from thegroup consisting of VdF/HFP copolymer, VdF/TFE/HFP copolymer, VdF/CTFEcopolymer, VdF/CTFE/TFE copolymer, VdF/PAVE copolymer, VdF/TFE/PAVEcopolymer, VdF/HFP/PAVE copolymer, VdF/HFP/TFE/PAVE copolymer,VdF/TFE/propylene (Pr) copolymer, VdF/ethylene (Et)/HFP copolymer, andcopolymer of VdF/fluoromonomer of formula (2). Further, the rubber ismore preferably one having at least one selected from the groupconsisting of TFE, HFP, and PAVE as comonomer(s) other than VdF.Preferable among these is at least one copolymer selected from the groupconsisting of VdF/HFP copolymer, VdF/TFE/HFP copolymer, copolymer ofVdF/fluoromonomer of formula (2), VdF/PAVE copolymer, VdF/TFE/PAVEcopolymer, VdF/HFP/PAVE copolymer, and VdF/HFP/TFE/PAVE copolymer. Morepreferable among these is at least one copolymer selected from the groupconsisting of VdF/HFP copolymer, VdF/HFP/TFE copolymer, copolymer ofVdF/fluoromonomer of formula (2), and VdF/PAVE copolymer. Particularlypreferable among these is at least one copolymer selected from the groupconsisting of VdF/HFP copolymer, copolymer of VdF/fluoromonomer offormula (2), and VdF/PAVE copolymer.

In the VdF/HFP copolymer, the composition of VdF/HFP is preferably (45to 85)/(55 to 15) (mol %), more preferably (50 to 80)/(50 to 20) (mol%), and further preferably (60 to 80)/(40 to 20) (mol %).

In the VdF/TFE/HFP copolymer, the composition of VdF/TFE/HFP ispreferably (30 to 80)/(4 to 35)/(10 to 35) (mol %).

In the VdF/PAVE copolymer, the composition of VdF/PAVE is preferably (65to 90)/(35 to 10) (mol %).

In the VdF/TFE/PAVE copolymer, the composition of VdF/TFE/PAVE ispreferably (40 to 80)/(3 to 40)/(15 to 35) (mol %).

In the VdF/HFP/PAVE copolymer, the composition of VdF/HFP/PAVE ispreferably (65 to 90)/(3 to 25)/(3 to 25) (mol %).

In the VdF/HFP/TFE/PAVE copolymer, the composition of VdF/HFP/TFE/PAVEis preferably (40 to 90)/(0 to 25)/(0 to 40)/(3 to 35) (mol %), and morepreferably (40 to 80)/(3 to 25)/(3 to 40)/(3 to 25) (mol %).

In the copolymer of VdF/fluoromonomer (2) of formula (2), the mol %ratio of VdF/fluoromonomer (2) units is preferably 85/15 to 20/80 andthe amount of monomer units other than the VdF and fluoromonomer (2)units is preferably 0 to 50 mol % of all of the monomer units; the mol %ratio of the VdF/fluoromonomer (2) units is more preferably 80/20 to20/80. The mol % ratio of the VdF/fluoromonomer (2) units is alsopreferably 85/15 to 50/50, and the amount of monomer units other thanthe VdF and fluoromonomer (2) units is also preferably 1 to 50 mol % ofall of the monomer units. The monomers other than the VdF andfluoromonomer (2) units are preferably the monomers listed above as thecomonomers for VdF, that is, TFE, HFP, PMVE, perfluoroethyl vinyl ether(PEVE), PPVE, CTFE, trifluoroethylene, hexafluoroisobutene, vinylfluoride, ethylene (Et), propylene (Pr), alkyl vinyl ether, monomersgiving a cross-linkable group, and a reactive emulsifier. Morepreferable among these are PMVE, CTFE, HFP, and TFE.

The TFE/propylene (Pr) fluororubber is a fluorocopolymer containing 45to 70 mol % of TFE and 55 to 30 mol % of propylene (Pr). In addition tothese two components, the rubber may further contain 0 to 40 mol % of aspecific third component (e.g. PAVE).

In the ethylene (Et)/HFP copolymer, the composition of Et/HFP ispreferably (35 to 80)/(65 to 20) (mol %), and more preferably (40 to75)/(60 to 25) (mol %).

In the Et/HFP/TFE copolymer, the composition of Et/HFP/TFE is preferably(35 to 75)/(25 to 50)/(0 to 15) (mol %), and more preferably (45 to75)/(25 to 45)/(0 to 10) (mol %).

Examples of the perfluoro fluororubber include those containingTFE/PAVE. The composition of TFE/PAVE is preferably (50 to 90)/(50 to10) (mol %), more preferably (50 to 80)/(50 to 20) (mol %), and furtherpreferably (55 to 75)/(45 to 25) (mol %).

Examples of the PAVE in this case include PMVE and PPVE. Each of thesemay be used alone, or any of these may be used in combination.

The fluororubber (A) preferably has a number average molecular weight Mnof 5,000 to 500,000, more preferably 10,000 to 500,000, and particularlypreferably 20,000 to 500,000.

Any perfluoro fluororubber or non-perfluoro fluororubber at least havinga TFE unit, a VdF unit, or a fluoromonomer unit of formula (1) may beused as the fluororubber (A) suitable for the peroxide cross-linksystem. In particular, a VdF rubber or a TFE/Pr rubber is preferable.

The above-described non-perfluoro fluororubber and perfluorofluororubber may be produced by a common method such as emulsionpolymerization, suspension polymerization, or solution polymerization.In particular, a polymerization method using an iodine (bromine)compound, which is known as iodine (bromine) transfer polymerization,can provide a fluororubber having a narrow molecular weightdistribution.

In order to provide a fluororubber composition having a low viscosity,for example, other species of fluororubbers may be blended with thefluororubber (A). Examples of other fluororubbers include low molecularweight liquid fluororubbers (number average molecular weight: 1,000 ormore), low molecular weight fluororubbers having a number averagemolecular weight of about 10,000, and fluororubbers having a numberaverage molecular weight of about 100,000 to about 200,000.

The listed monomers in the above non-perfluoro fluororubber andperfluoro fluororubber are examples of the main monomers of the rubber,and the main monomers may be suitably copolymerized with monomers givinga peroxide cross-linkable group. The monomer giving a peroxidecross-linkable group may be any monomer which can provide a suitablecross-linkable group depending on the production method. Examplesthereof include known polymerizable compounds and chain transfer agentswhich have an iodine atom, bromine atom, carbon-carbon double bond orthe like.

Examples of the monomer giving a preferable cross-linkable group includea compound represented by formula (3):CY¹ ₂═CY²R_(f) ²X¹  (3)wherein Y¹ and Y² each are a fluorine atom, hydrogen atom, or —CH₃;R_(f) ² is a linear or branched fluoroalkylene group which may have oneor more ethereal oxygen atoms and which may have one or more aromaticrings, and in which part or all of the hydrogen atoms are replaced byfluorine atoms; and X¹ is an iodine atom or a bromine atom. Specificexamples thereof include: iodine-containing monomers andbromine-containing monomers represented by formula (4):CY¹ ₂═CY²R_(f) ³CHR¹—X¹  (4)wherein Y¹, Y², and X¹ each are the same as defined above; R_(f) ³ is alinear or branched fluoroalkylene group which may have one or moreethereal oxygen atoms and in which part or all of the hydrogen atoms arereplaced by fluorine atoms, i.e., R_(f) ³ is a linear or branchedfluoroalkylene group in which part or all of the hydrogen atoms arereplaced by fluorine atoms, a linear or branched fluorooxyalkylene groupin which part or all of the hydrogen atoms are replaced by fluorineatoms, or a linear or branched fluoropolyoxyalkylene group in which partor all of the hydrogen atoms are replaced by fluorine atoms; R¹ is ahydrogen atom or a methyl group; and iodine-containing monomers andbromine-containing monomers represented by formulas (5) to (22):CY⁴ ₂═CY⁴(CF₂)_(n)—X¹  (5)wherein Y⁴s may be the same as or different from each other, and each ofthese is a hydrogen atom or a fluorine atom, and n is an integer of 1 to8;CF₂═CFCF₂R_(f) ⁴—X¹  (6)whereinR_(f) ⁴ is

OCF₂

_(n),

OCF(CF₃)

_(n)and n is an integer of 0 to 5;CF₂═CFCF₂(OCF(CF₃)CF₂)_(m)(OCH₂CF₂CF₂)_(n)OCH₂CF₂—X¹  (7)wherein m is an integer of 0 to 5, and n is an integer of 0 to 5;CF₂═CFCF₂(OCH₂CF₂CF₂)_(m)(OCF(CF₃)CF₂)_(n)OCF(CF₃)—X¹  (8)wherein m is an integer of 0 to 5, and n is an integer of 0 to 5;CF₂═CF(OCF₂CF(CF₃))_(m)O(CF₂)_(n)—X¹  (9)wherein m is an integer of 0 to 5, and n is an integer of 1 to 8;CF₂═CF(OCF₂CF(CF₃))_(m)—X¹  (10)wherein m is an integer of 1 to 5;CF₂═CFOCF₂(CF(CF₃)OCF₂)_(n)CF(—X¹)CF₃  (11)wherein n is an integer of 1 to 4;CF₂═CFO(CF₂)_(n)OCF(CF₃)—X¹  (12)wherein n is an integer of 2 to 5;CF₂═CFO(CF₂)_(n)—(C₆H₄)—X¹  (13)wherein n is an integer of 1 to 6;CF₂═CF(OCF₂CF(CF₃))_(n)OCF₂CF(CF₃)—X¹  (14)wherein n is an integer of 1 or 2;CH₂═CFCF₂O(CF(CF₃)CF₂O)_(n)CF(CF₃)—X¹  (15)wherein n is an integer of 0 to 5;CF₂═CFO(CF₂CF(CF₃)O)_(m)(CF₂)_(n)—X¹  (16)wherein m is an integer of 0 to 5, and n is an integer of 1 to 3;CH₂═CFCF₂OCF(CF₃)OCF(CF₃)—X¹  (17)CH₂═CFCF₂OCH₂CF₂—X¹  (18)CF₂═CFO(CF₂CF(CF₃)O)_(m)CF₂CF(CF₃)—X¹  (19)wherein m is an integer of 0 or greater;CF₂═CFOCF(CF₃)CF₂O(CF₂)_(n)—X¹  (20)wherein n is an integer of 1 or greater;CF₂═CFOCF₂OCF₂CF(CF₃)OCF₂—X¹  (21)CH₂═CH—(CF₂)_(n)X¹  (22)wherein n is an integer of 2 to 8.In formulas (5) to (22), X¹ is the same as defined above. Each of themonomers may be used alone, or any of these may be used in combination.

The iodine-containing monomer or the bromine-containing monomerrepresented by formula (4) is preferably an iodine-containingfluorinated vinyl ether represented by formula (23):

wherein m is an integer of 1 to 5, and n is an integer of 0 to 3. Morespecific examples thereof include the following monomers.

Preferable among these is ICH₂CF₂CF₂OCF═CF₂.

Specifically preferable examples of the iodine-containing monomer andthe bromine-containing monomer represented by formula (5) includeICF₂CF₂CF═CH₂ and I(CF₂CF₂)₂CF═CH₂.

Specifically preferable examples of the iodine-containing monomer andthe bromine-containing monomer represented by formula (9) includeI(CF₂CF₂)₂OCF═CF₂.

Specifically preferable examples of the iodine-containing monomer andthe bromine-containing monomer represented by formula (22) includeCH₂═CHCF₂CF₂I and I(CF₂CF₂)₂CH═CH₂.

Further, a bisolefin compound represented by formula:R²R³C═CR⁴—Z—CR⁵═CR⁶R⁷wherein R², R³, R⁴, R⁵, R⁶, and R⁷ may be the same as or different fromeach other, and each of these is H or a C1-C5 alkyl group; Z is a C1-C18linear or branched alkylene or cycloalkylene group which may have anoxygen atom and is preferably at least partially fluorinated, or a (per)fluoropolyoxyalkylene group, is also preferable as a monomer giving across-linkable group. The term “(per)fluoropolyoxyalkylene group” hereinmeans a fluoropolyoxyalkylene group or a perfluoropolyoxyalkylene group.

Z is preferably a C4-C12 (per)fluoroalkylene group, and R², R³, R⁴, R⁵,R⁶, and R⁷ each are preferably a hydrogen atom.

In the case that Z is a (per)fluoropolyoxyalkylene group, it ispreferably a (per)fluoropolyoxyalkylene group represented by formula:-(Q)_(p)-CF₂O—(CF₂CF₂O)_(m)—(CF₂O)_(n)—CF₂-(Q)_(p)-wherein Q is a C1-C10 alkylene group or a C2-C10 oxyalkylene group; p is0 or 1; and m and n are integers which give an m/n ratio of 0.2 to 5 anda molecular weight of the (per)fluoropolyoxyalkylene group of 500 to10,000, preferably 1,000 to 4,000. In this formula, Q is preferablyselected from —CH₂OCH₂— and —CH₂O(CH₂CH₂O)_(s)CH₂—wherein s=1 to 3.

Preferable examples of the bisolefin include CH₂═CH—(CF₂)₄—CH═CH₂,CH₂═CH—(CF₂)₆—CH═CH₂, and those represented by formula:CH₂═CH—Z¹—CH═CH₂wherein Z¹ is —CH₂OCH₂—CF₂O—(CF₂CF₂O)_(m)—(CF₂O)_(n)—CF₂—CH₂OCH₂—,wherein m/n is 0.5.

Preferable among these is3,3,4,4,5,5,6,6,7,7,8,8-dodecafluoro-1,9-decadiene represented asCH₂═CH—(CF₂)₆—CH═CH₂.

In the case that cross-linking is performed by the peroxide cross-linksystem employed in the present invention, particularly in the case thatthe cross-linking site has a carbon-carbon bond, the system is superiorin chemical resistance and steam resistance compared with the polyolcross-link system in which the cross-linking site has a carbon-oxygenbond and the polyamine cross-link system in which the cross-linking sitehas a carbon-nitrogen double bond.

From the viewpoint of cross-linkability, the peroxide cross-linkablefluororubber (A) is preferably a fluororubber having an iodine atomand/or a bromine atom at a cross-linking site. The amount of an iodineatom and/or a bromine atom is preferably 0.001 to 10% by mass, furtherpreferably 0.01 to 5% by mass, and particularly preferably 0.01 to 3% bymass.

From the viewpoint of processability, the fluororubber (A) preferablyhas a Mooney viscosity at 100° C. of within a range of 20 to 200, andfurther preferably 30 to 180. The Mooney viscosity is measured inaccordance with ASTM-D1646 and JIS K 6300.

Carbon Black (B)

The carbon black (B) is not particularly limited as long as it is acarbon black allowing the fluororubber composition of the presentinvention, containing the fluororubber (A), the peroxide cross-linkingagent (C), and the low-self-polymerizing cross-linking accelerator (D),to give a cross-linked fluororubber product having excellent heatresistance and excellent mechanical properties at high temperatures.

Examples of such a carbon black include furnace black, acetylene black,thermal black, channel black, and graphite. Specific examples thereofinclude SAF-HS(N₂SA: 142 m²/g, DBP: 130 ml/100 g), SAF (N₂SA: 142 m²/g,DBP: 115 ml/100 g), N234 (N₂SA: 126 m²/g, DBP: 125 ml/100 g), ISAF(N₂SA: 119 m²/g, DBP: 114 ml/100 g), ISAF-LS (N₂SA: 106 m²/g, DBP: 75ml/100 g), ISAF-HS(N₂SA: 99 m²/g, DBP: 129 ml/100 g), N339 (N₂SA: 93m²/g, DBP: 119 ml/100 g), HAF-LS (N₂SA: 84 m²/g, DBP: 75 ml/100 g),HAS-HS(N₂SA: 82 m²/g, DBP: 126 ml/100 g), HAF (N₂SA: 79 m²/g, DBP: 101ml/100 g), N351 (N₂SA: 74 m²/g, DBP: 127 ml/100 g), LI-HAF (N₂SA: 74m²/g, DBP: 101 ml/100 g), MAF-HS(N₂SA: 56 m²/g, DBP: 158 ml/100 g), MAF(N₂SA: 49 m²/g, DBP: 133 ml/100 g), FEF-HS(N₂SA: 42 m²/g, DBP: 160ml/100 g), FEF (N₂SA: 42 m²/g, DBP: 115 ml/100 g), SRF-HS(N₂SA: 32 m²/g,DBP: 140 ml/100 g), SRF-HS(N₂SA: 29 m²/g, DBP: 152 ml/100 g), GPF (N₂SA:27 m²/g, DBP: 87 ml/100 g), SRF (N₂SA: 27 m²/g, DBP: 68 ml/100 g),SRF-LS (N₂SA: 23 m²/g, DBP: 51 ml/100 g), FT (N₂SA: 19 m²/g, DBP: 42ml/100 g), and MT (N₂SA: 8 m²/g, DBP: 43 ml/100 g). Each of these carbonblacks may be used alone, or two or more of these may be used incombination.

Particularly preferable as the carbon black is a carbon black having anitrogen adsorption specific surface area (N₂SA) of 5 to 180 m²/g and adibutyl phthalate (DBP) oil absorption of 40 to 180 ml/100 g. If acarbon black used has high N₂SA and/or DBP value, the values of the lossmodulus E″ and the storage modulus E′ will be high.

If a carbon black having a nitrogen adsorption specific surface area(N₂SA) smaller than 5 m²/g is mixed into the rubber, the mechanicalproperties of the rubber tend to be poor. From this viewpoint, thenitrogen adsorption specific surface area (N₂SA) is preferably 10 m²/gor larger, more preferably 20 m²/g or larger, and particularlypreferably 25 m²/g or larger. The upper limit thereof is preferably 180m²/g because of the generally easy availability.

If a carbon black having a dibutyl phthalate (DBP) oil absorption ofsmaller than 40 ml/100 g is mixed into the rubber, the mechanicalproperties of the rubber tend to be poor. From this viewpoint, the DBPoil absorption is preferably 50 ml/100 g or higher, further preferably60 ml/100 g or higher, and particularly preferably 80 ml/100 g orhigher. The upper limit thereof is preferably 175 ml/100 g, and furtherpreferably 170 ml/100 g because of the generally easy availability.

The amount of the carbon black (B) is preferably 5 to 50 parts by massto 100 parts by mass of the fluororubber (A). Too large or too small anamount of the carbon black (B) tends to cause poor mechanical propertiesof a cross-linked product. For good balance of physical properties, theamount thereof is preferably 6 parts by mass or more, and morepreferably 10 parts by mass or more, but preferably 49 parts by mass orless, and more preferably 45 parts by mass or less, to 100 parts by massof the fluororubber (A).

The composition of the present invention, containing a pre-mixture ofthe fluororubber composition prepared from the fluororubber (A) and thecarbon black (B), further contains a cross-linking agent (C) and alow-self-polymerizing cross-linking accelerator (D).

The cross-linking agent (C) and the cross-linking accelerator (D) to beused can be appropriately selected according to the fluororubber (A) tobe cross-linked (for example, the copolymerization composition, presenceof the cross-linking group and the kind thereof), the specificapplication and usage pattern of the cross-linked product to beobtained, and mixing and other conditions.

Peroxide Cross-Linking Agents (C)

The cross-linking agent (C) may be any peroxide capable of easilygenerating a peroxy radical in the presence of heat or a redox system.Specific examples thereof include organic peroxides such as1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane,2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide,t-butylcumyl peroxide, dicumyl peroxide,α,α-bis(t-butylperoxy)-p-diisopropylbenzene,α,α-bis(t-butylperoxy)-m-diisopropylbenzene,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3, benzoyl peroxide,t-butylperoxybenzene, t-butylperoxybenzoate, t-butylperoxy maleic acid,and t-butylperoxyisopropyl carbonate. Preferable among these is2,5-dimethyl-2,5-di(t-butylperoxy)hexane or2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3.

The amount of the cross-linking agent (C) is preferably 0.01 to 10 partsby mass, and more preferably 0.1 to 9 parts by mass, to 100 parts bymass of the fluororubber (A). If the amount of the cross-linking agent(C) is less than 0.01 parts by mass, the fluororubber (A) is notcross-linked sufficiently. If the amount thereof exceeds 10 parts bymass, the balance of the physical properties tends to be poor.

Low-Self-Polymerizing Cross-Linking Accelerator (D)

The low-self-polymerizing cross-linking accelerator (D) in the presentinvention is a compound having a low self-polymerizing property, unliketriallyl isocyanurate (TAIC) that is well known as a cross-linkingaccelerator of the peroxide cross-link system. Use of such alow-self-polymerizing cross-linking accelerator (D) enables to give across-linked product having excellent mechanical properties at hightemperatures and fatigue properties (such as resistance to fatiguecaused by repetitive use) at high temperatures.

Examples of the cross-linking accelerator (D) include the followingcompounds:

which represents trimethallyl isocyanurate (TMAIC);

which represents p-quinonedioxime;

which represents p,p′-dibenzoylquinonedioxime;

which represents maleimide;

which represents N-phenylenemaleimide; and

which represents N,N′-phenylene bismaleimide.

A preferable cross-linking accelerator (D) among these is trimethallylisocyanurate (TMAIC).

The amount of the cross-linking accelerator (D) is 2.5 parts by mass orless, preferably 2.0 parts by mass or less, further preferably 1.5 partsby mass or less, further more preferably less than 1.5 parts by mass,and particularly preferably 1.0 part by mass or less, to 100 parts bymass of the fluororubber (A). The lower limit thereof is preferably 0.01parts by mass in terms of prevention of under-curing. If the amount ofthe cross-linking accelerator (D) exceeds 2.5 parts by mass, the fatigueproperties at high temperatures may be reduced.

The fluororubber composition may contain known cross-linkingaccelerators or co-cross-linking agents, such as TAIC, maleimide,N-phenylenemaleimide, N,N′-phenylene bismaleimide, p-quinonedioxime, andp,p′-dibenzoylquinonedioxime, in an amount of less than 1.5 parts bymass, preferably 1.0 part by mass or less, and more preferably 0.8 partsby mass or less, to 100 parts by mass of the fluororubber (A).

If necessary, the fluororubber composition of the present invention mayfurther contain common additives for rubber such as filler, processingaid, plasticizer, colorant, bonding aid, acid acceptor, pigment, flameretardant, lubricant, photo stabilizer, weather-resistant stabilizer,antistatic agent, ultraviolet absorber, antioxidant, release agent,foaming agent, perfume, oil, and softener, and other polymers such aspolyethylene, polypropylene, polyamide, polyester, and polyurethane tothe extent that the effects of the present invention are notdeteriorated.

Examples of the filler include: metal oxides such as calcium oxide,magnesium oxide, titanium oxide, and aluminum oxide; metal hydroxidessuch as magnesium hydroxide, aluminum hydroxide, and calcium hydroxide;carbonates such as magnesium carbonate, aluminum carbonate, calciumcarbonate, and barium carbonate; silicates such as magnesium silicate,calcium silicate, sodium silicate, and aluminum silicate; sulfates suchas aluminum sulfate, calcium sulfate, and barium sulfate; metal sulfidessuch as synthesized hydrotalcite; molybdenum disulfide, iron sulfide,and copper sulfide; diatomaceous earth, asbestos, lithopone (zincsulfide/barium sulfide), graphite, carbon fluoride, calcium fluoride,coke, fine particulate quartz, talc, powdery mica, Wollastonite, fibrouscarbon, fibrous aramid, various whiskers, fibrous glass, organicreinforcing agent, organic filler, polytetrafluoroethylene, mica,silica, celite, and clay. Further, examples of the acid acceptor includecalcium oxide, magnesium oxide, lead oxide, zinc oxide, magnesiumhydroxide, calcium hydroxide, aluminum hydroxide, and hydrotalcite. Eachof these may be used alone, or two or more of these may be appropriatelyused in combination. These may be added at any step in thelater-described mixing method; they are preferably added in mixing thefluororubber and the carbon black with a closed mixer or a roll mixer.

Examples of the processing aid include: higher fatty acids such asstearic acid, oleic acid, palmitic acid, and lauric acid; higher fattyacid salts such as sodium stearate and zinc stearate; higher fatty acidamides such as stearamide and oleamide; higher fatty acid esters such asethyl oleate; petroleum wax such as carnauba wax and ceresin wax;polyglycols such as ethylene glycol, glycerine, and diethylene glycol;aliphatic hydrocarbons such as vaseline and paraffin; silicone oils,silicone polymers, low molecular weight polyethylene, phthalic acidesters, phosphoric acid esters, rosin, (halogenated) dialkylamines,surfactants, sulfone compounds, fluorine-containing aids, and organicamine compounds.

In particular, the organic amine compound and the acid acceptor arepreferable additives because, in the case that they are blended inmixing the fluororubber (A) and the carbon black (B) with a closed mixeror a roll mixer, they improve reinforceability. Mixing is preferablycarried out at the highest temperature Tm upon mixing of 80 to 220° C.(in other words, mixing is preferably carried out under the conditionthat a mixed product has a highest temperature Tm of 80° C. to 220° C.while being mixed and being discharged. The same applies below).

Preferable examples of the organic amine compound include primary aminesrepresented as R¹NH₂, secondary amines represented as R¹R²NH, andtertiary amine represented as R¹R²R³N. R¹, R², and R³ may be the same asor different from each other and each of these is preferably a C1-C50alkyl group. The alkyl group may have a benzene ring as a functionalgroup, or may have a double bond and/or conjugated double bond. Further,the alkyl group may have a linear shape or a branched shape.

Examples of the primary amine include coconut amine, octyl amine, laurylamine, stearyl amine, oleyl amine, beef tallow amine,17-phenyl-heptadecylamine, octadeca-7,11-dienylamine,octadeca-7,9-dienylamine, octadec-9-enylamine, and7-methyl-octadec-7-enylamine. Examples of the secondary amine includedistearylamine. Examples of the tertiary amine includedimethyloctylamine, dimethyldecylamine, dimethyllaurylamine,dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, anddimethylbehenylamine. Particularly preferable are amines, especiallyprimary amines, having about 20 carbon atoms because they are easilyavailable and they improve reinforceability.

The amount of the organic amine compound is preferably 0.01 to 5 partsby mass to 100 parts by mass of the fluororubber (A). Too large anamount of the organic amine compound tends to cause difficulty inmixing, while too small an amount thereof tends to cause poorreinforceability. The amount with respect to 100 parts by mass of thefluororubber (A) is further preferably 0.1 parts by mass or more fromthe viewpoint of reinforceability and 4 parts by mass or less from theviewpoints of reinforceability and easy mixing. The acid acceptor ispreferably a metal hydroxide such as calcium hydroxide; a metal oxidesuch as magnesium oxide and zinc oxide; or hydrotalcite among theaforementioned examples from the viewpoint of reinforceability, forexample. Particularly, zinc oxide is preferable.

The amount of the acid acceptor is preferably 0.01 to 10 parts by massto 100 parts by mass of the fluororubber (A). Too large an amount of theacid acceptor tends to cause poor physical properties, while too smallan amount thereof tends to cause poor reinforceability. The amount withrespect to 100 parts by mass of the fluororubber (A) is furtherpreferably 0.1 parts by mass or more from the viewpoint ofreinforceability, while it is preferably 8 parts by mass or less, andmore preferably 5 parts by mass or less, from the viewpoints of physicalproperties and easy mixing.

The fluororubber composition can be produced by an ordinary rubbermixing method. Specific examples thereof include, but not limited to,the following methods.

(1) A method in which predetermined amounts of a fluororubber (A) and acarbon black (B), and if necessary an organic amine compound and/or anacid acceptor, are charged into a closed mixer, and then mixed at anaverage shear rate of a rotor of 50 to 1,000 (1/second), preferably 100to 1,000 (1/second), and further preferably 200 to 1,000 (1/second) sothat the highest mixing temperature Tm is 80° C. to 220° C. (preferably120° C. to 200° C.). Examples of the closed mixer include a pressurizingkneader, Banbury mixer, single screw mixer, and twin screw mixer.

(2) A method in which predetermined amounts of a fluororubber (A) and acarbon black (B), and if necessary an organic amine compound and/or anacid acceptor, are charged into a roll mixer, and then mixed under theconditions that the average shear rate of a rotor is 50 (1/second) orhigher and the highest mixing temperature Tm is 80° C. to 220° C.(preferably, 120° C. to 200° C.).

The fluororubber compositions obtained by the above methods (1) and (2)are free from components such as a cross-linking agent and across-linking accelerator. Further, the mixing of the methods (1) and(2) may be performed multiple times. In the case of performing themixing multiple times, the mixing conditions of the second andsubsequent mixing may be the same as those in the methods (1) and (2)except that the highest mixing temperature Tm is 140° C. or lower.

One example of the method for preparing a cross-linkable fluororubbercomposition used in the present invention is a method in which thefluororubber composition, obtained in the method (1) or (2) or byrepeating the method (1) or (2) multiple times, is further blend-mixedwith the cross-linking agent (C) and the cross-linking accelerator (D).

The cross-linking agent (C) and the cross-linking accelerator (D) may beblend-mixed at the same time, or the cross-linking accelerator (D) maybe first blend-mixed and then the cross-linking agent (C) may beblend-mixed. The conditions for mixing the cross-linking agent (C) andthe cross-linking accelerator (D) may be the same as those in themethods (1) and (2) except that the highest mixing temperature Tm is130° C. or lower.

Another example of the method for preparing a cross-linkablefluororubber composition is a method in which predetermined amounts ofthe fluororubber (A), the carbon black (B), the cross-linking agent (C),and the cross-linking accelerator (D) are charged into a roll mixer inan appropriate order, and then mixed under the conditions that theaverage shear rate of a rotor is 50 (1/second) or higher and the highestmixing temperature Tm is 130° C. or lower.

The preferable fluororubber composition of the present invention beforecross-linking has a difference δG′(G′(1%)−G′(100%)) of 120 kPa or higherand 3,000 kPa or lower, the difference determined by subtracting theshear modulus G′(100%) at 100% dynamic strain from the shear modulusG′(1%) at 1% dynamic strain in a dynamic viscoelasticity test with arubber process analyzer under the conditions of a measurement frequencyof 1 Hz and a measurement temperature of 100° C. In the case ofperforming the aforementioned pre-mixing (such as the mixing by theabove methods (1) and (2)), the pre-mixture preferably has the abovedifference δG′.

The difference δG′ is used as a standard for evaluating the property ofreinforcement of the rubber composition, and is determined by a dynamicviscoelasticity test with a rubber process analyzer.

A fluororubber composition having a difference δG′ in the range of 120kPa or higher and 3,000 kPa or lower has an advantageous normal state atroom temperature, mechanical properties at high temperatures, fatigueproperties at high temperatures, and the like.

The difference δG′ is preferably 150 kPa or higher, and furtherpreferably 160 kPa or higher, but preferably 2,800 kPa or lower, andfurther preferably 2,500 kPa or lower, for good properties such as anormal state at room temperature, mechanical properties at hightemperatures, and fatigue properties at high temperatures.

The fluororubber composition preferably has a difference δG′ in theabove range both before and after being mixed with the cross-linkingagent (C) and the cross-linking accelerator (D).

The mixing is preferably performed at an average shear rate of 50(1/second) to form a good carbon gel network reinforcing structure suchthat a fluororubber composition having the later-described specificdifference δG′ or a cross-linked product having the later-describedspecific loss modulus E″ and storage modulus E′ are obtained.

The average shear rate (1/second) is calculated by the followingformula.Average shear rate (1/second)=(π×D×R)/(60 (seconds)×c)wherein

D: rotor diameter or roll diameter (cm)

R: rotation rate (rpm)

c: tip clearance (cm, gap distance between rotor and casing or gapdistance between rolls)

In the present invention, the fluororubber composition may becross-linked and molded by an appropriately selected method. Examples ofthe method include common cross-linking and molding methods byextrusion, pressing, or injection. In the case of cross-linking andmolding a tube shaped product such as a hose, a cross-linking andmolding method, such as a molding method by extrusion or wrapped cureand a cross-linking method using a vulcanizing pan, is employed. If thefluororubber composition needs to be subjected to secondary curingdepending on the intended use of the cross-linked product to beobtained, the composition may be secondarily cured in an oven.

The obtained cross-linked fluororubber product has a particularlyexcellent normal state at room temperature and mechanical properties athigh temperatures in the case of having a loss modulus E″ at a tensilestrain of 1% of 400 kPa or higher and 6000 kPa or lower determined by adynamic viscoelasticity test (measurement mode: tensile, chuck distance:20 mm, frequency: 10 Hz, initial force: 157 cN, and measurementtemperature: 160° C.).

If the loss modulus E″ is within the above range, the cross-linkedproduct has a particularly excellent normal state at room temperatureand mechanical properties at high temperatures. The lower limit thereofis preferably 420 kPa, and more preferably 430 kPa. The upper limitthereof is preferably 5,900 kPa, and more preferably 5,800 kPa.

For improved mechanical properties at high temperatures, thecross-linked fluororubber product further preferably has a storagemodulus E′ of 1,500 kPa or higher and 20,000 kPa or lower determined bya dynamic viscoelasticity test (measurement mode: tensile, chuckdistance: 20 mm, measurement temperature: 160° C., tensile strain: 1%,initial force: 157 cN, and frequency: 10 Hz). The lower limit thereof ispreferably 1,600 kPa, and more preferably 1,800 kPa, while the upperlimit thereof is preferably 19,000 kPa, and more preferably 18,000 kPa.

The cross-linked fluororubber product preferably has an elongation atbreak at 160° C. of 100 to 700%, more preferably 110% or higher, andparticularly preferably 120% or higher, while preferably 680% or lower,and particularly preferably 650% or lower, because such a cross-linkedproduct is suitably used under high-temperature conditions.

The cross-linked fluororubber product preferably has a tensile strengthat break at 160° C. of 1 MPa or higher, further preferably 1.5 MPa orhigher, and particularly preferably 2 MPa or higher, while preferably 30MPa or lower, and particularly preferably 28 MPa or lower, because sucha cross-linked product is suitably used under high-temperatureconditions. The tensile strength at break and the elongation at breakare measured using #6 dumbbells in accordance with JIS-K 6251.

The cross-linked fluororubber product preferably has a tearing strengthat 160° C. of 3 to 30 kN/m, further preferably 4 kN/m or higher, andparticularly preferably 5 kN/m or higher, while preferably 29 kN/m orlower, and particularly preferably 28 kN/m or lower, because such across-linked product is suitably used under high-temperature conditions.

The cross-linked fluororubber product preferably has an elongation atbreak at 200° C. of 100 to 700%, further preferably 110% or higher, andparticularly preferably 120% or higher, while preferably 680% or lower,and particularly preferably 650% or lower, because such a cross-linkedproduct is suitably used under high-temperature conditions.

The cross-linked fluororubber product preferably has a tensile strengthat break at 200° C. of 1 to 30 MPa, further preferably 1.5 MPa orhigher, and particularly preferably 2 MPa or higher, while preferably 29MPa or lower, and particularly preferably 28 MPa or lower, because sucha cross-linked product is suitably used under high-temperatureconditions.

The cross-linked fluororubber product preferably has a tearing strengthat 200° C. of 3 to 30 kN/m, further preferably 4 kN/m or higher, andparticularly preferably 5 kN/m or higher, while preferably 29 kN/m orlower, and particularly preferably 28 kN/m or lower, because such across-linked product is suitably used under high-temperature conditions.

The cross-linked fluororubber product of the present invention can beused for various applications, particularly suitably for the followingapplications.

(1) Hose

A hose may be a monolayer hose consisting of the cross-linkedfluororubber product obtainable by cross-linking and molding thefluororubber composition of the present invention, or may be amultilayer hose having a laminated structure with other layers.

Examples of the monolayer hose include exhaust gas hoses, EGR hoses,turbo charger hoses, fuel hoses, brake hoses, and oil hoses.

Examples of the multilayer hose also include exhaust gas hoses, EGRhoses, turbo charger hoses, fuel hoses, brake hoses, and oil hoses.

Turbo systems are usually provided for diesel engines. In the turbosystem, exhaust gas discharged from an engine is sent to a turbine sothat the turbine is turned. Turning of the turbine drives a compressorcoupled with the turbine, and the compressor increases the compressionratio of the air supplied to the engine; as a result, the output ofpower increases. The turbo system, which utilizes exhaust gas from anengine and generates a high power, contributes to downsizing of anengine, low fuel consumption of an automobile, and purification ofexhaust gas.

A turbo charger hose is used in the turbo system as a hose for sendingcompressed air into the engine. In order to effectively use the limitedengine-room space, a rubber hose which is excellent in flexibility andsoftness is advantageous. Typically used hoses have a multilayerstructure that an inner layer comprises a rubber (especially afluororubber) layer excellent in heat-aging resistance and oilresistance and an outer layer comprises a silicone rubber or an acrylicrubber. However, the conditions of the engine and its vicinities such asthe engine room are severe due to high temperature and vibration. Thus,the hose requires not only excellent heat-aging resistance but alsoexcellent mechanical properties at high temperatures.

Hoses satisfy these required characteristics at high levels using across-linked fluororubber layer obtainable by cross-linking and moldingthe fluororubber composition of the present invention into a monolayeror multilayer rubber layer, and thus provide a turbo charger hose havingexcellent properties.

In multilayer hoses other than the turbo charger hose, layers made ofother materials may be layers made of other rubbers, thermoplastic resinlayers, fiber-reinforced layers, and metal foil layers, for example.

In the case that chemical resistance and flexibility are particularlyrequired, the other rubbers are preferably at least one selected fromthe group consisting of acrylonitrile-butadiene rubber and hydrogenatedrubber thereof, rubber blend of acrylonitrile-butadiene rubber andpolyvinyl chloride, fluororubber, epichlorohydrin rubber, EPDM, andacrylic rubber. They more preferably include at least one selected fromthe group consisting of acrylonitrile-butadiene rubber and hydrogenatedrubber thereof, rubber blend of acrylonitrile-butadiene rubber andpolyvinyl chloride, fluororubber, and epichlorohydrin rubber.

Further, the thermoplastic resin is preferably a thermoplastic resincomprising at least one selected from the group consisting offluororesin, polyamide resin, polyolefin resin, polyester resin,polyvinyl alcohol resin, polyvinyl chloride resin, and polyphenylenesulfide resin. The thermoplastic resin is more preferably athermoplastic resin comprising at least one selected from the groupconsisting of fluororesin, polyamide resin, polyvinyl alcohol resin, andpolyphenylene sulfide resin.

In the case of forming a multilayer hose, surface treatment may beoptionally performed. The surface treatment is not particularly limitedas long as it allows bonding. Examples thereof include dischargingtreatment such as plasma discharge and corona discharge, and wettreatment such as treatment with a metallic sodium/naphthalene solution.Further, priming is suitable as surface treatment. Priming can beperformed in accordance with a common method. In the case of priming,the surface of a fluororubber which is not surface-treated may betreated. Still, it is more effective to perform priming after priortreatment such as plasma discharge, corona discharge, or treatment witha metallic sodium/naphthalene solution.

Hoses produced from the cross-linked product of the present inventionmay be suitably used in the following fields.

In the fields relating to semiconductor production, e.g. semiconductorproducing devices, liquid crystal panel producing devices, plasma panelproducing devices, plasma-addressed liquid crystal panels, fieldemission display panels, and solar battery substrates, such a hose maybe used as a hose for devices under high-temperature conditions such asCVD devices, dry etching devices, wet etching devices, oxidationdiffusion devices, sputtering devices, asking devices, washing devices,ion implanting devices, and gas discharging devices.

In the automobile field, the hose can be used as a hose in peripheraldevices of engines and automatic transmissions, such as an EGR hose, anexhaust gas hose, a fuel hose, an oil hose, and a brake hose, as well asa turbo charger hose.

Furthermore, the hose can be used in the fields of aircraft, rockets andshipping, chemical plants, analysis/physical and chemical appliances,food plant appliances, nuclear plant appliances, and the like.

(2) Sealing Material

Sealing materials can be suitably used in the following fields.

Sealing materials may be used, for example, for vehicles, specificallyin the engine body, main driving system, valve gear system, lubricantand cooling system, fuel system, and air intake and exhaust system, ofthe engine; transmissions of the drive system; the steering system ofthe chassis; the braking system; and the basic electrical components,controlling electric components, and accessory electrical components. Insuch a field, the sealing material is required to have heat resistance,oil resistance, fuel oil resistance, engine antifreeze coolantresistance, and steam resistance. Examples of such a sealing materialinclude gaskets and contact or non-contact packings (e.g. self-sealingpackings, piston rings, split ring packings, mechanical seals, oilseals).

The sealing material used for the engine body of a vehicle engine is notparticularly limited, and examples thereof include cylinder headgaskets, cylinder head cover gaskets, oil pan packings, general gaskets,O-rings, packings, and timing belt cover gaskets.

Examples of the sealing material used for the main driving system of avehicle engine include, but not particularly limited to, shaft sealssuch as a crank shaft seal and a cam shaft seal.

Examples of the sealing material used for the valve gear system of avehicle engine include, but not particularly limited to, valve stem oilseals for an engine valve, and valve seats of a butterfly valve.

Examples of the sealing material used for the lubricant and coolingsystem of a vehicle engine include, but not particularly limited to,seal gaskets for an engine oil cooler.

Examples of the sealing material used for the fuel system of a vehicleengine include, but not particularly limited to, oil seals for a fuelpump, filler seals and tank packings for a fuel tank, connector O-ringsfor a fuel tube, injector cushion rings, injector seal rings, andinjector O-rings for a fuel injection device, flange gaskets for acarburetor, and sealing materials for EGR.

Examples of the sealing material used for the air intake and exhaustsystem of a vehicle engine include, but not particularly limited to,intake manifold packings and exhaust manifold packings for a manifold,throttle body packings for a throttle, and turbine shaft seals for aturbo charger.

Examples of the sealing material used for the transmissions of a vehicleinclude, but not particularly limited to, bearing seals, oil seals,O-rings, and packings for a transmission; and O-rings and packings foran automatic transmission.

Examples of the sealing material used for the braking system of avehicle include, but not particularly limited to, oil seals, O-rings,packings, piston cups (rubber cups) of master cylinders, caliper seals,and boots.

Examples of the sealing material used for the accessory electricalcomponent of a vehicle include, but not particularly limited to, O-ringsand packings for a car air-conditioner.

The sealing material is particularly suitable as a sealing material(bush) for a sensor, and more suitable as a sealing material for anoxygen sensor, a sealing material for a nitrogen oxide sensor, and asealing material for a sulfur oxide sensor. O-rings herein may be squarerings.

The sealing material may be applied to any field other than the field ofvehicles. The sealing material can be used in a wide range of fieldssuch as fields of aircraft, rocket, shipping, oil well drilling (e.g.packer seal, seal for MWD, seal for LWD), chemical products (e.g.plants), medical products (e.g. drugs), photographing (e.g. developingmachines), printing (e.g. printing machines), coating (e.g. coatingfacility), analysis/physical and chemical appliances, food plantappliances, nuclear plant appliances, steals (e.g. steel plateprocessing equipment), general industries, electrics, fuel cells,electronic components, and forming in place.

Examples of such a sealing material include packings, O-rings, and othersealing materials having oil resistance, chemical resistance, heatresistance, steam resistance or weather resistance in transportationfacilities such as ships and boats, and aircrafts; similar packings,O-rings, and other sealing materials in oil well drilling; similarpackings, O-rings, and other sealing materials in chemical plants;similar packings, O-rings, and other sealing materials in food plantappliances and food appliances (including household products); similarpackings, O-rings, and other sealing materials in nuclear plantappliances; and similar packings, O-rings, and other sealing materialsin general industrial components.

(3) Belt

The cross-linked fluororubber product of the present invention can besuitably used for the following belts.

That is, the cross-linked fluororubber product can be used for a belt ofa power transmission belt (including flat belts, V belts, V-ribbedbelts, and synchronous belts) or a belt for conveyance (conveyer belt).Further, In the fields relating to semiconductor production, e.g.semiconductor producing devices, liquid crystal panel producing devices,plasma panel producing devices, plasma-addressed liquid crystal panels,field emission display panels, and solar battery substrates, thecross-linked fluororubber product may be used for a belt for devicesunder high-temperature conditions such as CVD devices, dry etchingdevices, wet etching devices, oxidation diffusion devices, sputteringdevices, asking devices, washing devices, ion implanting devices, andgas discharging devices.

Examples of the flat belt include flat belts for high-temperaturecomponents such as ones arranged around the engine of an agriculturalmachine, a machine tool, an industrial machine, or the like. Examples ofthe conveyer belt include conveyer belts for conveying bulks andgranules such as coal, crushed stones, earth and sand, mineral, and woodchips at high temperatures; conveyer belts used in a blast furnace orthe like in iron works; and conveyer belts for use at high temperaturesin a precision-instruments assembly plant, a food factory, or the like.Examples of the V belt and the V-ribbed belt include V belts andV-ribbed belts for agricultural machines, general machinery (e.g. OAequipment, a printing machine, business-use drier), and vehicles.Examples of the synchronous belt include synchronous belts such astransmission belts of transfer robots, and transmission belts for foodmachines and machine tools; and synchronous belts for vehicles, OAequipment, medical use, and printing machines. Specific examples of thesynchronous belt for a vehicle include timing belts.

In multilayer belts, layers made of other materials may be layers madeof other rubbers, thermoplastic resin layers, fiber-reinforced layers,canvas, and metal foil layers, for example.

In the case that chemical resistance and flexibility are particularlyrequired, other rubbers preferably include at least one selected fromthe group consisting of acrylonitrile-butadiene rubber and hydrogenatedrubber thereof, rubber blend of acrylonitrile-butadiene rubber andpolyvinyl chloride, fluororubber, epichlorohydrin rubber, EPDM, andacrylic rubber. They more preferably include at least one selected fromthe group consisting of acrylonitrile-butadiene rubber and hydrogenatedrubber thereof, rubber blend of acrylonitrile-butadiene rubber andpolyvinyl chloride, fluororubber, and epichlorohydrin rubber.

Further, the thermoplastic resin is preferably a thermoplastic resincomprising at least one selected from the group consisting offluororesin, polyamide resin, polyolefin resin, polyester resin,polyvinyl alcohol resin, polyvinyl chloride resin, and polyphenylenesulfide resin. The thermoplastic resin is more preferably athermoplastic resin comprising at least one selected from the groupconsisting of fluororesin, polyamide resin, polyvinyl alcohol resin, andpolyphenylene sulfide resin.

In the case of forming a multilayer belt, surface treatment may beoptionally performed. The surface treatment is not particularly limitedas long as it allows bonding. Examples thereof include dischargingtreatment such as plasma discharge and corona discharge, and wettreatment such as treatment with a metallic sodium/naphthalene solution.Further, priming is suitable as surface treatment. Priming can beperformed in accordance with a common method. In the case of priming,the surface of a fluororubber which is not surface-treated may betreated. Still, it is more effective to perform priming after priortreatment such as plasma discharge, corona discharge, or treatment witha metallic sodium/naphthalene solution.

(4) Vibration-Insulating Rubber

The cross-linked fluororubber product of the present invention satisfiesthe required characteristics of a vibration-insulating rubber at highlevels using the cross-linked fluororubber product as a monolayer ormultilayer rubber layer, and thus provides a vibration-insulating rubberfor a vehicle which has excellent properties.

In multilayer vibration-insulating rubber other than the one for avehicle, layers made of other materials may be layers made of otherrubbers, thermoplastic resin layers, fiber-reinforced layers, and metalfoil layers, for example.

In the case that chemical resistance and flexibility are particularlyrequired, other rubbers preferably include at least one selected fromthe group consisting of acrylonitrile-butadiene rubber and hydrogenatedrubber thereof, rubber blend of acrylonitrile-butadiene rubber andpolyvinyl chloride, fluororubber, epichlorohydrin rubber, EPDM, andacrylic rubber. They more preferably include at least one selected fromthe group consisting of acrylonitrile-butadiene rubber and hydrogenatedrubber thereof, rubber blend of acrylonitrile-butadiene rubber andpolyvinyl chloride, fluororubber, and epichlorohydrin rubber.

Further, the thermoplastic resin is preferably a thermoplastic resincomprising at least one selected from the group consisting offluororesin, polyamide resin, polyolefin resin, polyester resin,polyvinyl alcohol resin, polyvinyl chloride resin, and polyphenylenesulfide resin. The thermoplastic resin is more preferably athermoplastic resin comprising at least one selected from the groupconsisting of fluororesin, polyamide resin, polyvinyl alcohol resin, andpolyphenylene sulfide resin.

In the case of forming a multilayer vibration-insulating rubber, surfacetreatment may be optionally performed. The surface treatment is notparticularly limited as long as it allows bonding. Examples thereofinclude discharging treatment such as plasma discharge and coronadischarge, and wet treatment such as treatment with a metallicsodium/naphthalene solution. Further, priming is suitable as surfacetreatment. Priming can be performed in accordance with a common method.In the case of priming, the surface of a fluororubber which is notsurface-treated may be treated. Still, it is more effective to performpriming after prior treatment such as plasma discharge, coronadischarge, or treatment with a metallic sodium/naphthalene solution.

(5) Diaphragm

The cross-linked fluororubber product of the present invention issuitable for the diaphragms described below.

Examples of the diaphragms include those for vehicle engines,specifically those used in the fuel system, exhaust system, brakingsystem, drive system, and ignition system, which need to have heatresistance, oxidation resistance, fuel resistance, and low gaspermeability.

Examples of the diaphragms used in the fuel system of a vehicle engineinclude: diaphragms for fuel pumps, diaphragms for carburetors,diaphragms for pressure regulators, diaphragms for pulsation dampers,diaphragms for ORVR, diaphragms for canisters, and diaphragms for autofuel cocks.

Examples of the diaphragms used in the exhaust system of a vehicleengine include: diaphragms for waste gates, diaphragms for actuators,and diaphragms for EGR.

Examples of the diaphragms used in the braking system of a vehicleengine include diaphragms for air braking.

Examples of the diaphragms used in the drive system of a vehicle engineinclude diaphragms for oil pressure.

Examples of the diaphragms used in the ignition system of a vehicleengine include diaphragms for distributors.

Examples of the diaphragms in addition to those for vehicle enginesincludes: diaphragms for general pumps, diaphragms for valves,diaphragms for filter press, diaphragms for blower, diaphragms for airconditioners, diaphragms for control equipments, diaphragms for watersupply, diaphragms for pumps transferring hot water used for hot-watersupply and the like, diaphragms for high-temperature steam, diaphragmsfor semiconductor devices (for example, diaphragms for transferringchemicals used in a manufacturing process), diaphragms forfood-processing devices, diaphragms for liquid storage tanks, diaphragmsfor pressure switches, diaphragms used oil exploration and oil drilling(for example, diaphragms for lubricant oil supply, such as oil drillbits), diaphragms for gas appliances such as instantaneous gas waterheaters and gas meters, diaphragms for accumulators, diaphragms for airsprings such as suspensions, diaphragms for screw feeders for ships andboats, and diaphragms for medical artificial hearts, which need to haveheat resistance, oil resistance, chemical resistance, steam resistance,and low gas permeability.

EXAMPLES

The present invention will be described referring to, but not limitedto, the following examples.

Measurement methods of physical properties adopted in the presentinvention are as follows.

(1) Dynamic Viscoelasticity Test

(A) Dynamic Viscoelasticity Measurement Before Cross-Linking (ShearModulus G′)

Measurement method of difference δG′ between shear modulus G′(1%) at 1%dynamic strain and shear modulus G′(100%) at 100% dynamic strain

The viscoelasticity is measured using a rubber process analyzer (model:RPA 2000) produced by Alpha Technology Co., Ltd. at 100° C. and 1 Hz.

(B) Dynamic Viscoelasticity Measurement of Cross-Linked Product (StorageModulus E′ and Loss Modulus E″)

Measurement device: Dynamic viscoelasticity measurement device DVA-220(IT Keisoku Seigyo K. K.)

Measurement Conditions

Specimen: cross-linked rubber cuboid having a size of 3 mm in width×2 mmin thickness

Measurement mode: tensile

Chuck distance: 20 mm

Measurement temperature: 160° C.

Tensile strain: 1%

Initial force: 157 cN

Frequency: 10 Hz

(2) Tensile Strength at Break, Elongation at Break

The test devices to be used are RTA-1T produced by Orientec Co., Ltd.and AG-I produced by Shimadzu Corporation. The tensile strength at breakand the elongation at break are measured using #6 dumbbells at a strainrate of 500 mm/min with a chuck distance of 50 mm in accordance withJIS-K 6251. The measuring temperatures are 25° C. and 160° C.

(3) Repeated High-Temperature Tensile Test

The test device used is AG-I produced by Shimadzu Corporation. Thetensile conditions are #6 dumbbells, a chuck distance of 50 mm, and achuck movement speed of 500 mm/min in accordance with JIS-K 6251. Thetemperature is set to 160° C. The sample was 300%-stretched repeatedly,and the number of cycles until the breaking of the sample was counted.

(4) Mooney Viscosity (ML₁₊₁₀(100° C.))

The Mooney viscosity was determined in accordance with ASTM-D 1646 andJIS K 6300. The measurement temperature is 100° C.

In the examples and comparative examples, the following fluororubber,carbon black, peroxide cross-linking agent, and low-self-polymerizingcross-linking accelerator were used.

(Fluororubber A1)

Pure water (44 L), a 50% aqueous solution ofCH₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)COONH₄ (8.8 g), and a 50% aqueous solutionof F(CF₂)₃COONH₄ (176 g) were charged into a 82-L stainless-steelautoclave, and the air inside the system was sufficiently replaced withnitrogen gas. The mixture was stirred at 230 rpm and heated to 80° C.,and then monomers were injected under pressure so that the initialmonomer composition in the tank was VdF/HFP=50/50 mol % and the internalpressure was 1.52 MPa. A polymerization initiator solution prepared bydissolving APS (1.0 g) into pure water (220 ml) was injected underpressure using nitrogen gas, and thus a reaction was initiated. When theinternal pressure was down to 1.42 MPa as the polymerization proceeded,a mixed monomer (VdF/HFP=78/22 mol %), which is an additional monomer,was injected under pressure until the internal pressure reached 1.52MPa. Then, a diiodine compound I(CF₂)₄I (73 g) was injected underpressure. While the pressure was repeatedly increased and decreased, anaqueous solution of APS (1.0 g)/pure water (220 ml) was injected underpressure using nitrogen gas every 3 hours so as to allow thepolymerization reaction to proceed. As 14,000 g in total of the mixedmonomer was added, unreacted monomers were removed and the autoclave wascooled down. Thereby, a fluororubber dispersion with a solid contentconcentration of 23.1% by mass was obtained. NMR analysis on thefluororubber showed that the copolymer composition was VdF/HFP=78/22(mol %), and the Mooney viscosity (ML₁₊₁₀(100° C.)) was 55. Thisfluororubber was named Fluororubber A1.

(Fluororubber A2)

A fluororubber dispersion with a solid content concentration of 23.2% bymass was obtained through polymerization under the same conditions asthose for the production method of Fluororubber A1, except that, theinitial monomer composition in the tank was changed toVdF/TFE/HFP=19/11/70 mol %, the additional monomer was changed toVdF/TFE/HFP=51/20/29 mol %, a 50% aqueous solution of F(CF₂)₃COONH₄ waschanged to a 50% aqueous solution of F(CF₂)_(s)COONH₄, the amount of thediiodine compound I(CF₂)₄I was changed to 45 g, and after addition of atotal of 630 g of the monomer mixture, 74 g of ICH₂CF₂CF₂OCF═CF₂ wasfed. NMR analysis on the fluororubber showed that the copolymercomposition was VdF/TFE/HFP=52/22/26 (mol %), and the Mooney viscosity(ML₁₊₁₀(100° C.)) was 80. This fluororubber was named Fluororubber A2.

(Carbon Black)

(B1): ISAF carbon black SEAST 6 (Tokai Carbon Co., Ltd.; N₂SA=119 m²/g;DBP oil absorption=114 ml/100 g)

(Peroxide Cross-Linking Agent)

(C1): PERHEXA 25B (NOF Corporation)

(Self-Polymerizing Cross-Linking Accelerator)

(D1): Trimethallyl isocyanurate (TMAIC, Nippon Kasei Chemical Co., Ltd.)

(D2): Triallyl isocyanurate (TAIC, Nippon Kasei Chemical Co., Ltd.)

(D3): N,N′-phenylene bismaleimide (Sigma-Aldrich Corp.)

(Processing Aid)

(E1): Stearylamine (FARMIN 86T, Kao Corp.)

(Acid Acceptor)

(F1): Zinc oxide (#1, Sakai Chemical Industry Co., Ltd.)

Example 1

Fluororubber (A1) (100 parts by mass) was mixed with carbon black (B1)(20 parts by mass), stearylamine (E1) (0.5 parts by mass), and zincoxide (F1) (1.0 part by mass) using a mixer (TD 35 100 MB, Toshin Co.,Ltd., rotor diameter: 30 cm, tip clearance: 0.1 cm) under the mixingconditions of front rotor speed: 29 rpm and back rotor speed: 24 rpm.Thereby, a fluororubber precompound (A) was prepared. The maximumtemperature of the discharged mixed product was 168° C.

The obtained fluororubber precompound (A) was subjected to the dynamicviscoelasticity test by a rubber process analyzer (RPA 2000). Thedifference δG′ determined was 591 kPa.

Thereafter, the fluororubber precompound (A) (121.5 parts by mass) wasmixed with the peroxide cross-linking agent PERHEXA 25B (C1) (1.0 partby mass), the low-self-polymerizing cross-linking accelerator TMAIC (D1)(0.58 parts by mass), and the processing aid stearylamine (E1) (0.5parts by mass) using an 8-inch open roll mixer (KANSAI ROLL Co., Ltd.)under the mixing conditions of front roll speed: 21 rpm, back rollspeed: 19 rpm, and gap distance between rolls: 0.1 cm. Thereby, afluororubber full compound (PR) was prepared. The maximum temperature ofthe discharged mixed product was 71° C.

Reference Example 1

A fluororubber full compound was produced under the same conditions asthose for Example 1, except that, TAIC (D2) was used as thelow-self-polymerizing cross-linking accelerator instead of TMAIC (D1),and the amount of the cross-linking accelerator was changed from 0.58parts by mass to 0.5 parts by mass. The maximum temperature of thedischarged mixed product was 73° C.

The fluororubber full compounds obtained in Example 1 and ReferenceExample 1 were pressed at 160° C. for 60 minutes to be cross-linked,whereby cross-linked products of 2-mm-thick sheet-shaped specimens wereproduced.

The respective cross-linked specimens were measured for the tensilestrength at break and elongation at break at 25° C. Also, the specimenswere measured for the tensile strength at break and the elongation atbreak at 160° C., and were subjected to the repeated high-temperaturetensile test. Table 1 shows the results.

The cross-linked products were also measured for the dynamicviscoelasticity. Table 1 shows the results.

Example 2

A fluororubber full compound was produced under the same conditions asthose for Example 1, except that the amount of the low-self-polymerizingcross-linking accelerator TMAIC (D1) was changed from 0.58 parts by massto 0.9 parts by mass. The maximum temperature of the discharged mixedproduct was 72° C. A cross-linked sheet was produced under the sameconditions as those for Example 1, and various physical properties weredetermined in the same way as in Example 1. Table 1 shows the results.

Example 3

Fluororubber (A1) (100 parts by mass) was mixed with carbon black (B1)(25 parts by mass), stearylamine (E1) (0.5 parts by mass), and zincoxide (F1) (1.0 part by mass) using a mixer (TD 35 100 MB, Toshin Co.,Ltd., rotor diameter: 30 cm, tip clearance: 0.1 cm) under the mixingconditions of front rotor speed: 29 rpm and back rotor speed: 24 rpm.Thereby, a fluororubber precompound (B) was prepared. The maximumtemperature of the discharged mixed product was 174° C.

The obtained fluororubber precompound (B) was subjected to the dynamicviscoelasticity test by a rubber process analyzer (RPA 2000). Thedifference δG′ determined was 990 kPa.

Thereafter, the fluororubber precompound (B) (126.5 parts by mass) wasmixed with the peroxide cross-linking agent PERHEXA 25B (C1) (1.5 partby mass), the low-self-polymerizing cross-linking accelerator TMAIC (D1)(0.58 parts by mass), and the processing aid stearylamine (E1) (0.5parts by mass) using an 8-inch open roll mixer (KANSAI ROLL Co., Ltd.)under the mixing conditions of front roll speed: 21 rpm, back rollspeed: 19 rpm, and gap distance between rolls: 0.1 cm. Thereby, afluororubber full compound (PR) was prepared. The maximum temperature ofthe discharged mixed product was 76° C.

A cross-linked sheet was produced under the same conditions as those forExample 1, and various physical properties were determined in the sameway as in Example 1. Table 1 shows the results.

Example 4

Fluororubber (A2) (100 parts by mass) was mixed with carbon black (B1)(20 parts by mass), stearylamine (E1) (0.5 parts by mass), and zincoxide (F1) (1.0 part by mass) using a mixer (TD 35 100 MB, Toshin Co.,Ltd., rotor diameter: 30 cm, tip clearance: 0.1 cm) under the mixingconditions of front rotor speed: 29 rpm and back rotor speed: 24 rpm.Thereby, a fluororubber precompound (C) was prepared. The maximumtemperature of the discharged mixed product was 170° C.

The obtained fluororubber precompound (C) was subjected to the dynamicviscoelasticity test by a rubber process analyzer (RPA 2000). Thedifference δG′ determined was 621 kPa.

Thereafter, the fluororubber precompound (C) (121.5 parts by mass) wasmixed with the peroxide cross-linking agent PERHEXA 25B (C1) (0.5 partby mass), the low-self-polymerizing cross-linking accelerator TMAIC (D1)(0.3 parts by mass), and the processing aid stearylamine (E1) (0.5 partsby mass) using an 8-inch open roll mixer (KANSAI ROLL Co., Ltd.) underthe mixing conditions of front roll speed: 21 rpm, back roll speed: 19rpm, and gap distance between rolls: 0.1 cm. Thereby, a fluororubberfull compound (PR) was prepared. The maximum temperature of thedischarged mixed product was 71° C.

A cross-linked sheet was produced under the same conditions as those forExample 1, and various physical properties were determined in the sameway as in Example 1. Table 1 shows the results.

Example 5

A fluororubber full compound was produced under the same conditions asthose for Example 1, except that, N,N′-phenylene bismaleimide (D3) wasused as the low-self-polymerizing cross-linking accelerator instead ofTMAIC (D1), and the amount of the cross-linking accelerator was changedfrom 0.58 parts by mass to 0.9 parts by mass, and the amount of thecross-linking agent was changed from 1.0 parts by mass to 4.0 parts bymass. The maximum temperature of the discharged mixed product was 65° C.A cross-linked sheet was produced under the same conditions as those forExample 1, and various physical properties were determined in the sameway as in Example 1. Table 1 shows the results.

Comparative Example 1

A fluororubber full compound was produced under the same conditions asthose for Example 1, except that the amount of the low-self-polymerizingcross-linking accelerator TMAIC (D1) was changed from 0.58 parts by massto 3.0 parts by mass. The maximum temperature of the discharged mixedproduct was 71° C. A cross-linked sheet could not be produced under thesame conditions as those for Example 1 because of under-curing.

TABLE 1 Reference Comparative Example 1 Example 2 Example 3 Example 4Example 5 Example 1 Example 1 Composition (parts by mass) Fluororubberprecompound (A) 121.5 121.5 121.5 121.5 121.5 Fluororubber precompound(B) 126.5 Fluororubber precompound (C) 121.5 TMAIC 0.58 0.9 0.58 0.3 —3.0 TAIC — 0.5 N,N′-phenylene bismaleimide 0.9 Cross-linking agent 1.01.0 1.5 0.5 4.0 1.0 1.0 Stearylamine 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Presscross-linking conditions 160° C., 160° C., 160° C., 160° C., 160° C.,160° C., 160° C., 60 min 60 min 60 min 60 min 60 min 60 min 60 minMechanical properties of cross-linked product Measuring temperature: 25°C. Tensile strength at break (MPa) 16.3 13.2 16.6 20.3 12.3 18.2 —Elongation at break (%) 920 970 830 670 860 740 — Measuring temperature:160° C. Tensile strength at break (MPa) 3.3 2.5 5 4.8 3.7 4 — Elongationat break (%) 600 720 580 336 690 430 — Repeated high-temperature tensiletest (160° C.) Number of cycles until breaking >50 >50 42 20 37 15 —Dynamic viscoelasticity test (160° C.) Storage modulus E′ (kPa) 52343857 6394 6866 3521 5984 — Loss modulus E″ (kPa) 1206 1085 1810 14861021 1472 —

The invention claimed is:
 1. A fluororubber composition comprising: aperoxide cross-linkable fluororubber (A); a carbon black (B); a peroxidecross-linking agent (C); and a low-self-polymerizing cross-linkingaccelerator (D), wherein the carbon black (B) is a carbon black having anitrogen adsorption specific surface area (N₂SA) of 20 m²/g to 180 m²/g,and the low-self-polymerizing cross-linking accelerator (D) is at leastone selected from the group consisting of trimethylallyl isocyanurate,p-quinonedioxime, p,p′-dibenzoylquinonedioxime, maleimide,N-phenylenemaleimide and N,N′-phenylene bismaleimide, and wherein to 100parts by mass of the fluororubber (A), the amount of the carbon black(B) is 5 to 50 parts by mass, the amount of the cross-linking agent (C)is 0.01 to 10 parts by mass, and the amount of the cross-linkingaccelerator (D) is 0.01 to 1.0 parts by mass.
 2. The fluororubbercomposition according to claim 1, wherein the carbon black (B) is acarbon black having a nitrogen adsorption specific surface area (N₂SA)of 20 to 180 m²/g and a dibutyl phthalate (DBP) oil absorption of 40 to180 ml/100 g.
 3. The fluororubber composition according to claim 1,wherein the fluororubber (A) is a vinylidene fluoride copolymer rubber,a tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer rubber, ora tetrafluoroethylene/propylene copolymer rubber.
 4. The fluororubbercomposition according to claim 1, wherein the cross-linking accelerator(D) is trimethallyl isocyanurate.
 5. The fluororubber compositionaccording to claim 1, wherein the fluororubber composition beforecross-linking has a difference δG′ (G′(1%)−G′(100%)) of 120 kPa orhigher and 3,000 kPa or lower, the difference determined by subtractingthe shear modulus G′(100%) at 100% dynamic strain from the shear modulusG′(1%) at 1% dynamic strain in a dynamic viscoelasticity test with arubber process analyzer (RPA) under the conditions of a measurementfrequency of 1 Hz and a measurement temperature of 100° C.
 6. Across-linked fluororubber product obtained by cross-linking thefluororubber composition according to claim
 1. 7. The cross-linkedfluororubber product according to claim 6, wherein the cross-linkedfluororubber product has a loss modulus E″ of 400 kPa or higher and6,000 kPa or lower determined by a dynamic viscoelasticity test underthe conditions of a measurement temperature of 160° C., a tensile strainof 1%, an initial force of 157 cN, and a frequency of 10 Hz.
 8. Thecross-linked fluororubber product according to claim 6, wherein thecross-linked fluororubber product has a storage modulus E′ of 1,500 kPaor higher and 20,000 kPa or lower determined by a dynamicviscoelasticity test under the conditions of a measurement temperatureof 160° C., a tensile strain of 1%, an initial force of 157 cN, and afrequency of 10 Hz.